b3dCollisionNZ

Returns Z component of collision surface normal (north-south direction, forward-back). Takes entity, index. Returns NZ (normal Z, -1.0 to +1.0). Gets collision[index].normal.GetZ(). Use for directional response, reflection calculations, impact orientation. Unit vector component. Flipped per entity. Thread-safe, O(1), returns 0.0 if out of bounds.